Laser apparatus and optical transmitter

Abstract

A laser apparatus includes a semiconductor laser of which a drive condition is controlled according to a plurality of types of drive currents and a controller which controls the drive condition such that a sum of the drive currents is equal to or less than a predetermined threshold value.

What is claimed is: 
     
       1. A laser apparatus comprising:
 a semiconductor laser of which a drive condition is controlled according to a plurality of types of drive currents; 
 a controller configured to control the drive condition such that a sum of the drive currents is equal to or less than a predetermined threshold value, and to control the drive condition to increase one or more of the drive currents when one or more of the other drive currents is decreased; 
 a thermoelectric cooler configured to control a temperature of the semiconductor laser at a setting temperature; and 
 a temperature sensor configured to detect an environmental temperature at which the semiconductor laser operates, wherein 
 the semiconductor laser includes a semiconductor amplification region configured to amplify a light beam emitted from a gain region of the semiconductor laser, 
 the plurality of types of drive currents includes a first drive current for the thermoelectric cooler and a second drive current for the semiconductor amplification region, 
 the control of the drive condition includes temperature control performed by the thermoelectric cooler to control the temperature of the semiconductor laser at the setting temperature, and 
 the temperature control is performed such that a sum of the first and second drive currents is equal to or less than the threshold value according to the environmental temperature detected by the temperature sensor. 
 
     
     
       2. The laser apparatus according to  claim 1 , further comprising a memory configured to store a setting value of the setting temperature per environmental temperature, the setting value of the setting temperature being obtained in advance based on a first relationship and a second relationship and satisfying a condition that the sum is the equal to or less than the threshold value, wherein
 the first relationship is a relationship between the setting temperature for the environmental temperature and, the first drive current, 
 the second relationship is a relationship between the setting temperature for the environmental temperature and temperature dependent loss of output light power of the semiconductor laser corresponding to the temperature control, and 
 the controller is configured to read from the memory the setting value corresponding to the environmental temperature detected by the temperature sensor to perform the temperature control according to the read setting value. 
 
     
     
       3. A laser apparatus comprising:
 a semiconductor laser of which a drive condition is controlled according to a plurality of types of drive currents; 
 a controller configured to control the drive condition such that a sum of the drive currents is equal to or less than a predetermined threshold value: 
 a thermoelectric cooler configured to control a temperature of the semiconductor laser at a setting temperature; 
 a temperature sensor configured to detect an environmental temperature at which the semiconductor laser operates; and 
 a monitor configured to monitor output light power of the semiconductor laser, wherein 
 the semiconductor laser includes a semiconductor amplification region configured to amplify a light beam emitted from a gain region of the semiconductor laser, 
 the plurality of types of drive currents includes a first drive current for the thermoelectric cooler, a second drive current for the semiconductor amplification region and a third drive current for the gain region, 
 the control of the drive condition includes temperature control to control the setting temperature of the semiconductor laser at the setting temperature by controlling the first drive current, and output light power control to control one or both of the second and third drive currents such that the output light power monitored by the monitor becomes target power, and 
 the temperature control and the output light power control are performed such that a sum of the first to third drive currents is maintained at the threshold value or less, based on the environmental temperature detected by the temperature sensor and wavelength dependent gain of the semiconductor amplification region corresponding to a setting of a light emission wavelength of the semiconductor laser. 
 
     
     
       4. The laser apparatus according to  claim 3 , further comprising a memory configured to store a setting value of the setting temperature and a setting value of the third drive current per environmental temperature, the setting values being obtained in advance based on a first relationship, a second relationship and a third relationship and satisfying the condition that the sum is equal to or less than the threshold value, wherein
 the first relationship is a relationship between the setting temperature for the environmental temperature and the first drive current, 
 the second relationship is a relationship between the setting temperature for the environmental temperature and temperature dependent loss of output light power of the semiconductor laser corresponding to the temperature control, 
 the third relationship is a relationship of an amplification gain with respect to the light emission wavelength of the semiconductor amplification region, and 
 the controller is configured to read from the memory each of the setting values corresponding to the environmental temperature detected by the temperature sensor and a setting of a light emission wavelength of the semiconductor laser to control the setting temperature of the semiconductor laser and perform constant control of the output light power, based on the read setting values. 
 
     
     
       5. A laser apparatus comprising:
 a semiconductor laser of which a drive condition is controlled according to a plurality of types of drive currents; 
 a controller configured to control the drive condition such that a sum of the drive currents is equal to or less than a predetermined threshold value; and 
 a monitor configured to monitor output light power of the semiconductor laser, wherein 
 the semiconductor laser includes a semiconductor amplification region configured to amplify a light beam emitted from a gain region of the semiconductor laser, 
 the plurality of types of drive currents includes a second drive current for the semiconductor amplification region and a third drive current for the gain region, 
 the control of the drive condition includes output light power control to control one or both of the second and third drive currents such that the output light power monitored by the monitor becomes target power, and 
 the output light power control is performed such that a sum of the second and third drive currents is maintained at the threshold value or less, based on wavelength dependent gain of the semiconductor amplification region corresponding to a setting of a light emission wavelength of the semiconductor laser. 
 
     
     
       6. The laser apparatus according to  claim 5 , further comprising a memory configured to store a setting value of the third drive current per light emission wavelength, the setting value being obtained in advance based on a relationship between the light emission wavelength and an amplification gain with respect to the light emission wavelength of the semiconductor amplification region,
 wherein the controller is configured to read from the memory the setting value corresponding to a setting of the light emission wavelength of the semiconductor laser to perform constant control of the output light power. 
 
     
     
       7. An optical transmitter comprising:
 a semiconductor laser of which a drive condition is controlled according to a plurality of types of drive currents; 
 a controller configured to control the drive condition such that a sum of the drive currents is equal to or less than a predetermined threshold value, and to control the drive condition to increase one or more of the drive currents when one or more of the other drive currents is decreased; 
 a thermoelectric cooler configured to control a temperature of the semiconductor laser at a setting temperature; and 
 a temperature sensor configured to detect an environmental temperature at which the semiconductor laser operates, wherein 
 the semiconductor laser includes a semiconductor amplification region configured to amplify a light beam emitted from a gain region of the semiconductor laser, 
 the plurality of types of drive currents includes a first drive current for the thermoelectric cooler and a second drive current for the semiconductor amplification region, 
 the control of the drive condition includes temperature control performed by the thermoelectric cooler to control the temperature of the semiconductor laser at the setting temperature, and 
 the temperature control is performed such that a sum of the first and second drive currents is equal to or less than the threshold value according to the environmental temperature detected by the temperature sensor. 
 
     
     
       8. An optical transmitter comprising:
 a semiconductor laser of which a drive condition is controlled according to a plurality of types of drive currents; 
 a controller configured to control the drive condition such that a sum of the drive currents is equal to or less than a predetermined threshold value; 
 a thermoelectric cooler configured to control a temperature of the semiconductor laser at a setting temperature; 
 a temperature sensor configured to detect an environmental temperature at which the semiconductor laser operates; and 
 a monitor configured to monitor output light power of the semiconductor laser, wherein 
 the semiconductor laser includes a semiconductor amplification region configured to amplify a light beam emitted from a gain region of the semiconductor laser, 
 the plurality of types of drive currents includes a first drive current for the thermoelectric cooler, a second drive current for the semiconductor amplification region and a third drive current for the gain region, 
 the control of the drive condition includes temperature control to control the setting temperature of the semiconductor laser at the setting temperature by controlling the first drive current, and output light power control to control one or both of the second and third drive currents such that the output light power monitored by the monitor becomes target power, and 
 the temperature control and the output light power control are performed such that a sum of the first to third drive currents is maintained at the threshold value or less, based on the environmental temperature detected by the temperature sensor and wavelength dependent gain of the semiconductor amplification region corresponding to a setting of a light emission wavelength of the semiconductor laser.